The reaction layer on the surface of titanium plates and titanium rods is the main factor affecting the physical and chemical properties of titanium workpieces. Before processing, it is necessary to completely remove the surface contamination layer and defect layer. So, how to deal with surface defects?
1. Sandblasting:
The sandblasting treatment of titanium wire castings is generally better using white corundum spray, and the sandblasting pressure is smaller than that of non precious metals, generally controlled below 0.45MPa. Because when the injection pressure is too high, the sand particles impact the titanium surface and generate intense sparks. The temperature increase can react with the titanium surface, forming secondary pollution and affecting surface quality. The time is 15-30 seconds, and only the sand adhering to the surface of the casting, the surface sintered layer, and some oxidation layer can be removed. The remaining surface reaction layer structures should be quickly removed by chemical pickling.
2. Pickling:
Acid washing can quickly and completely remove the surface reaction layer without generating contamination from other elements on the surface. Both HF-HCL and HF-HNO3 pickling solutions can be used for titanium pickling, but HF-HCL pickling solutions have a larger hydrogen absorption capacity, while HF-HNO3 pickling solutions have a smaller hydrogen absorption capacity. The concentration of HNO3 can be controlled to reduce hydrogen absorption, and the surface can be polished. Generally, the concentration of HF is around 3% -5%, and the concentration of HNO3 is around 15% -30%.
3. Chemical polishing:
During chemical polishing, the goal of leveling and polishing is achieved through the redox reaction of metals in a chemical medium. Its advantage is that chemical polishing is independent of the hardness, polishing area, and structural shape of the metal. All parts that come into contact with the polishing solution are polished, without the need for special and complex equipment. It is easy to operate and is more suitable for polishing complex titanium denture brackets. However, the process parameters of chemical polishing are difficult to control, requiring a good polishing effect on dentures without affecting their accuracy. A better titanium chemical polishing solution is prepared with HF and HNO3 in a certain proportion. HF is a reducing agent that can dissolve titanium metal and play a leveling role. When the concentration is less than 10%, HNO3 plays an oxidizing role, preventing excessive dissolution and hydrogen absorption of titanium, while also producing a brightening effect. Titanium polishing solution requires high concentration, low temperature, and short polishing time (1-2 minutes).
4. Electrolytic polishing:
Also known as electrochemical polishing or anodic dissolution polishing, due to the low conductivity and strong oxidation performance of titanium alloy tubes, it is almost impossible to polish titanium using aqueous acidic electrolytes such as HF-HO4 and HF-H2SO4 series electrolytes. After applying an external voltage, the titanium anode immediately oxidizes, making anodic dissolution impossible. However, using anhydrous chloride electrolyte at low voltage has a good polishing effect on titanium. Small specimens can achieve mirror polishing, but for complex restorations, the goal of complete polishing cannot be achieved.
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